402: Sedimentary Petrology Lecture 14: Siliciclastic Diagenesis Instructor: Dr. Douglas W. Haywick UNIVERSITY OF SOUTH ALABAMA
402: Sedimentary Petrology
Lecture 14: Siliciclastic Diagenesis
Instructor: Dr. Douglas W. Haywick
UNIVERSITY OF SOUTH ALABAMA
Last Time (online)
Immature siliciclastic sediment and sedimentary rocks
Pictorial overview
Alluvial fans
Braided rivers
1 km
Alluvial Fans
Alluvial Fans
Best developed in arid regions
Best developed in tectonically active areas
From Walker, R.G. 1980. Facies Models. Geological Association of Canada
Lateral fining
Alluvial Fans
Best developed in arid regions
Best developed in tectonically active areas
Formed primarily through the action of water flow, but there are also mass flow deposits
Debris flows, fluidized flow and “sieve” deposits
Alluvial Fans
Chalk Board
Wal
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R.G
. and
Jam
es, N
.P.,
1992
. Fac
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Alluvial Fan Facies
Wal
ker,
R.G
. and
Jam
es, N
.P.,
1992
. Fac
ies
Mod
els.
Res
pons
e to
Sea
Le
vel C
hang
e.G
eolo
gica
l Ass
ocia
tion
of C
anad
a, 4
09p.
Alluvial Fan Facies
Alluvial Fans - sed. sections
Nemec, W. and Steel, R.J., 1984. Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass-flow deposits. In Koster, E.H. and Steel, R. eds), Sedimentology of Gravels and Conglomerates. Canadian Society of Petroleum Geologists Mem. 10, 1-31.
Nemec, W. and Steel, R.J., 1984. Alluvial and coastal conglomerates: their significant features and some comments on gravelly mass-flow deposits. In Koster, E.H. and Steel, R. eds), Sedimentology of Gravels and Conglomerates. Canadian Society of Petroleum Geologists Mem. 10, 1-31.
Alluvial Fans - sed. sections
Braided Streams Best developed in alluvial plains with “steep gradients” (1 to 3
degrees of slope); frequently in mountainous areas
http://www.ak.nrcs.usda.gov/technical/images/Braided%20River.jpg
Braided Streams Facies
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.
Gravel beds comprise the majority of channel and bar facies, but sand and mud are also common (flood plain facies)
Braided Streams Facies
Braided Stream –sed sections
Walker, R.G. and James, N.P., 1992. Facies Models. Response to Sea Level Change. Geological Association of Canada, 409p.
Today’s Agenda
Siliciclastic Diagenesis
•Dia-what?
•Cementation
•Alteration/mineral replacement
Diagenesis
Diagenesis: all changes to sediment/sedimentary rock from the time of deposition to the onset of metamorphism.
Diagenesis Metamorphism
Deposition Chlorite
Diagenesis
Diagenesis: all changes to sediment/sedimentary rock from the time of deposition to the onset of metamorphism.
•Burrowing •Boring •Encrustation
•Compaction •Cementation •Dissolution •Pressure solution
•Replacement •Recrystallization •Fracturing •Etc.
Diagenesis
Cementation
Cementation
Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks.
Matrix: fine-grained* material deposited simultaneously with larger particles. Generally appears as darker-coloured detritus between grains
Cement: a chemical precipitate between grains formed from pore-water long after deposition.
Matrix versus Cement
Cementation
Cementation: pore-filling minerals precipitated into voids within sediment/sedimentary rocks.
•Quartz •Chert •Chalcedony •Opal
•Hematite •Limonite •Phosphate •Clay •Glauconite
•Calcite •Aragonite •Mg-calcite •Dolomite •Siderite •Etc.
Cement Homogeneous Chemically pure Lines pores Specific fabrics Multiphased zoned
300 µm SEM
Quartz grain cement
Cementation
Cement • Homogeneous
• Chemically pure • Lines pores
• Specific fabrics • Multiphased
• zoned
50 µm PPL
Quartz cement Hematite cement
Cementation
Cement • Homogeneous
• Chemically pure • Lines pores
• Specific fabrics • Multiphased
• zoned
300 µm SEM Quartz grain
Quartz overgrowth cement
Cementation
Cementation
Cements come in numerous fabrics
•Fibrous •Bladed •Acicular •Pendant •Concentric •Poikilotopic
•Botryoidal •Drusy •Syntaxial •Micritic •Massive •etc.
Chalk board (McIlreath and Morrow, 1990)
ppl
Cementation
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Quartz overgrowth
cement
0.25 mm
ppl xn
glauconite
Cementation
ppl xn
Cementation
ppl xn
chalcedony
Cementation
300 µm
ppl xn
chalcedony
Cementation
300 µm opal
250 µm XN
Cement
Origins
Cement
Phreatic
Vadose
Origins Cements precipitate from
pore waters (vadose and phreatic zones)
Cement
Phreatic
Vadose
Origins Cements precipitate from
pore waters (vadose and phreatic zones)
Timing ranges from synsedimentary to burial
Cement
Phreatic
Vadose
Origins Cements precipitate from
pore waters (vadose and phreatic zones)
Timing ranges from synsedimentary to burial
Cements give clues about water chemistry (pH, Eh, etc) and environment
Cement
Origins Cements can also be
precipitated directly on (and below) the sea floor
Shallow Marine Phreatic
Sea floor
Deep Marine Phreatic
Combination of potassium ferricyanide and Alizarin red-S
Carbonate Staining
Red/Pink: distinguishes CaCO3 from other minerals
5 mm PPL
Alteration/Mineral Replacement
Mineral Replacement: a change in composition from one mineral to another (fabric preserving versus fabric destroying)
Alteration/Mineral Replacement
Plagioclase to calcite
(XN, 2 mm FOV)
Mineral Replacement: a change in composition from one mineral to another (fabric preserving versus fabric destroying)
Alteration/Mineral Replacement
Plagioclase to sericite (muscovite)
(XN, 1 mm FOV)
http://www.union.edu/PUBLIC/GEODEPT/COURSES/petrology/ig_minerals/sericite1-X-40x.JPG
Upcoming Stuff Homework
1) Write 4; Lit Review (due Thursday Feb 23rd) 2) Peer Review (due Friday Feb 24th )
3) Grain Size project (due Thursday March 2nd ; Team Grade)
Lab Today TS 3 Diagenesis thin section lab (due Thursday Feb 23rd )
Online Lecture Nothing this week
Thursday Activity:
Activity 6-discussion on paper (Write 4 exercise )
GY 402: Sedimentary Petrology
Lecture 14: Siliciclastic Diagenesis
Instructor: Dr. Doug Haywick [email protected]
This is a free open access lecture, but not for commercial purposes. For personal use only.